Concepts and Principles of Sensorimotor System Functions

Concepts and Principles of Sensorimotor System Functions - This article will explain the sensorimotor system. Through this article is expected to be able to understand the concepts of sensorimotor system according to experts.

Three Principles of Sensorimotor Functions

The Hierarchically Organized Sensorimotor System

Operating system sensorimotor can be analogized as a large company that is efficient, controlled by commands that come down through the levels of hierarchy → association cortex associated as president of the company (the highest level) to the muscles or "workers" (level low).
The superiority of hierarchical organizations is that the higher levels in the hierarchy are left free to perform more complex functions.
This sensorimotor system is a parallel hierarchical system → a hierarchical system whose signals flow between different levels through multiple paths.
This parallel structure allows the association cortex to apply control over lower levels of hierarchy in more than one way.
The sensorimotor hierarchy is also characterized by functional segregation → each level of the sensorimotor hierarchy tends to consist of distinct units (neural structures), each of which performs different functions.
Thus, the sensorimotor system is a parallel and functionally organized hierarchical system.
The main difference between the sensory system and the sensorimotor system → the direction of the primary information flow → within the sensory system, information flows up through the hierarchy, whereas in the sensorimotor system, information flows down.

Concepts and Principles of Sensorimotor System Functions_

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Motor Output Guided by Sensory Input

Eyes, balance organs, and receptors in the skin, muscles, and joints all monitor the body's responses, and they feed that information into sensorimotor circuits.
In most cases, sensory feedback plays an important role in directing the continuity of the various responses it produces.
The only responses that are not usually influenced by sensory feedback are ballistic movements → short, all-or-none, and high-speed movements, for example the movement of swat flies.
Many adjustments in motor output occur in response to sensory feedback that is unconsciously controlled by lower sensorimotor hierarchy levels without higher levels of involvement.

Learn to Change the Nature and Locus of Sensorimotor Controls

During the early stages of motor learning, each individual response is performed under conscious control → after much practice, individual responses become organized into continuously integrated sequential actions that flow smoothly and are adjusted by sensory feedback without conscious regulation, For example: typing skills, swimming, knitting, playing basketball etc.

Sensorimotor Association Cortex

There are 2 main sensorimotor association cortex regions: the posterior parietal association cortex, and the dorsolateral prefrontal association cortex.
The posterior parietal cortex and the dorsolateral prefrontal cortex each consist of several different regions, each of which has different functions.

Posterior Parietal Association Cortex

Before an effective movement begins, it takes certain information → the nervous system must know the initial position of the parts of the body to be moved, and it must also know the position of the external object with whom the body will interact.
The posterior parietal association cortex → plays an important role in integrating these two kinds of information and in directing attention.
In turn, much of the posterior parietal cortex output goes to the motor cortex areas (located in the frontal cortex) → to the dorsolateral prefrontal association cortex, to various regions of the secondary motor cortex, and to the frontal eye field (a small area of the prefrontal cortex that controls movement Eye-movements).
Damage to the posterior parietal cortex can result in various sensorimotor deficits → deficits in perception and memory of spatial relationships, deficits in reaching and holding accurately, deficits in controlling eye movements and deficits in concentration.
Apraxia (apraxia) → involuntary motion disturbance that can not be attributed to a simple motor deficit or to any deficit in comprehension and motivation → patients have difficulty in performing certain movements when they are asked to do so, especially when the movement is out of context. But they can often do the same moves easily under natural conditions, when they are not thinking about the action.
Despite its bilateral symptoms, apraxia is often caused by unilateral damage → the posterior parietal lobe or on its connectors.
Contralateral neglect → interference with the patient's ability to respond to stimuli on one side of the body opposite (contralateral) with the side of the brain lesion, without any sensory deficit or simple motor deficit.
Patients with contralateral neglect often behave as if the left side of the world is missing, and they often do not know that they have a problem.
Most patients with contralateral neglect have difficulty responding to things on the left → also called egocentric lef t → partially defined by gravitational coordinates.

The Dorsolateral Prefrontal Association Cortex

The dorsolateral prefrontal association cortex → accepts projections of the posterior parietal cortex, and sends these projections to the secondary motor cortex areas, to the primary motor cortex, and to the frontal eye field.
The dorsolateral prefrontal cortex appears to play a role in the evaluation of external stimuli and the initiation of intentional reactions to it.
The activity of some neurons depends on the characteristics of the object, the activity of some other neurons depends on the location of the object, and the activity of some other neurons depends on the combination of the two. The activity of other dorsolateral prefrontal neurons is related to the response, and not to the object.
The dorsolateral prefrontal neuron response properties suggest that the decision to initiate deliberate movement can be taken in this cortical region, depending on the critical interaction with the posterior parietal cortex.

Secondary Motor Cortex

Secondary motor cortex → regions that receive much of its input from the association cortex and send many of its output to the primary motor cortex.
Two secondary regions of the secondary motor cortex are known → the supplementary motor area and the premotoric cortex.
Suplementary motor area → covers the top of the frontal lobe and extends, down the medial surface into the longitudinal fissure.
The → premotoric cortex flows in strips from the supplementary motor regions to the lateral fissures.
Electrical stimulation of a secondary motor cortex area usually triggers a complex movement, which often involves both sides of the body and the neurons in a secondary motor cortex area often becomes more active just before the initiation of a deliberate and active motion as long as the motion is performed.
Secondary motor cortex areas are thought to be involved in programming certain motion patterns after receiving general instructions from the dorsolateral prefrontal cortex.
Mirror neurons → neurons that shoot when an individual performs certain hand movements that lead to a goal or when he sees the same purpose-directed movements performed by others, for example: these neurons shoot when an ape reaches an object (eg , Toys) but do not shoot when the ape reaches another object → these neurons shoot as hard as the monkey observes the experimenter taking the same object.
This discovery provides a possible mechanism for social cognition (knowledge of the perceptions, ideas, and intentions of others) → mapping the actions of others into their own repertoire of actions will facilitate social understanding, cooperation, and imitation / imitation.

Primary Motorcort Cortex

Primary motor cortex → lies in the frontal lobe prefrontal gyrus → this cortex is the main convergence point of cortical sensorimotor signals, and is the primary starting point, but not the only, of the sensorimotor signals of the cerebral cortex.
Primary motor cortex is organized somatotopically → according to body map.
The somatotopic arrangement of the human primary motor cortex is commonly referred to as motor homunculus .
Each location in the primary motor cortex receives sensory feedback from receptors in the muscles and joints affected by that location.
The function of each primary motor cortex neuron → codes the direction of movement.
The shooting of the primary motor cortical neuron correlates with the direction of the resulting motion rather than with the direction of force generated to produce movement.
It is believed that every location in the primary motor cortex controls a muscle in the contralateral part of the body, and that each neuron produces movement in a particular direction.
Signals from each location in the primary motor cortex are highly divergent so that any given point has the ability to carry a body part (eg arm) to the target location, regardless of its original position. In addition, it can be concluded that the sensorimotor system is plastic.
Large lesions in the primary motor cortex can disrupt the patient's ability to move one part of his body (eg, one finger) independently → astereognosia → can reduce the speed, accuracy, and strength of the patient's movement.

Serebelum and Ganglia Basal

Cerebellum

The cerebellum receives information from the primary and secondary motor cortex → information about the motor signals descending from the brainstem brain nucleus, and feedback from motor responses through the somatosensoric and vestibular systems → cerebellum is thought to compare these three input sources and correct the movements The ongoing deviation from the desired source.
By performing this function, the cerebellum is believed to play a major role in motor learning, especially in studying sequence sequences whose timing is a critical factor.
Consequences of cerebral damage → the patient loses his ability to precisely control the direction, strength, velocity, and amplitude of motion and his ability to adapt various patterns of motor output with changing conditions. It is difficult to maintain a fixed posture (eg, standing), and attempts to do so often give rise to tremors. There is also considerable damage to balance, walking, and eye movement control.

Ganglia Basalis

Basal ganglia do not contain as many neurons as cerebellum, but in some sense they are more complex.
Basal ganglia are a complex set of heterogeneous nuclei that are complexly interconnected → like cerebellum, they operate modulatoric functions.
Basal ganglia do not contribute fibra to descending motor pathways , but are part of the neural loops that receive cortical input from various cortical regions and retransmit through the thalamus to different regions of the motor cortex
Traditional views of basal ganglia → as well as cerebellum, basal ganglia play a role in modulating motor output. Now, basal ganglia are also suspected of being involved in various cognitive functions → they project into cortical regions known to possess various cognitive functions.

Motorways that Flow from Top to Bottom

Signals neural dikonduktasikan of the primary motor cortex into neuron-motor neuron spinal cord through four different paths → 2 lines running from top to bottom in the dorsolateral spinal cord ( tract corticospinal dorsolateral and tracts kortikorubrospinal dorsolateral ) and 2 run from the top to Downwards in the medial region of the spinal cord medial ( ventromedial corticospinal tract and ventromedial spinal cortical-brainstem tract ).
Signals that are coupled through these pathways work together in controlling deliberate movement.
The four motor tracts are from the cerebral cortex → allegedly mediate movement on purpose, but have different functions.

Sensorimotor Spinal Circuit Circuits

Spinal motorcycles of motor spine show considerable complexity in function, regardless of signals coming from the brain.

Muscles

Each motor unit consists of a single motor neuron and all individual skeletal muscle fibers in which it is observed → when the motor neuron fires, all the muscle fibers of the unit contract together.
A skeletal muscle consists of hundreds of thousands of muscle fibers like a yarn united in a strong membrane and attached to the bone by a tendon
Acetyloline released by motor neurons in the neuromuscular junction → activating the end-plate motor in every muscle fiber → causes the fibers to contract.
All motor neurons that conserve the muscle fibers of the motor pool .
Skeletal muscle fibers are often thought to consist of two basic types: fast and slow.
Fast muscle fibers → contract and slack quickly → despite being able to generate great power, they get tired quickly because they are not well-ventilated.
Slow muscle fibers - though slower than weaker, are able to perform longer contractions because their vascularization is richer.
Flexor → works to bend or flex the joints.
Extensor → works to straighten or stretch out.
Every 2 muscles that contract produce the same movement, flexion and extension → synergistic muscles.
Muscles that work opposite, such as biceps and triceps → antagonistic muscles.
Muscle contractions that can increase the tension applied to the 2 bones without shortening and pulling together → isometric contractions.
Contractions that can shorten and pull together together → dynamic contractions.
Tension in a muscle can be increased by increasing the number of neurons in shooting motor pools , by increasing the firing rates of shooting neurons, or commonly used ones, with a combination of both.
The activity of skeletal muscles is monitored by two types of receptors → Golgi tendon organs and muscle spindles.
Golgin tendon organs respond to increased muscle tension (ie withdrawal of the muscle in the tendon in question), but not at all sensitive to changes in muscle length.
Muscle-spindle responds to changes in muscle length, but does not respond to muscle tension.
Each spindle of muscle has a threadlike intrafusal muscle, which is inhibited by intrafusal motor neurons.
Without intrafusal motor input, a spindle of muscle relaxes each time the contracted skeletal muscle. In a sagging state, the spindle muscle will not be able to do its job, that is responding to small changes in the length of the extrafusal muscle.

Reflexive Reflexes

Leg extension caused by tapping → patellar tendon reflex → stretch reflex → reflex generated by external stretching force in a muscle.
The mechanism by which reflexes are used to defend limb stability.

Fascinating Reflexes

Reflex withdrawal ( withdrawal reflex ) → when a painful stimulus on the hand → is recorded in the motor neurons of the flexor muscles of the arm for about 1.6 milliseconds.

Central Sensorimotor Programs

The central sensorimotor program theory says that unless the highest level in the sensorimotor system has certain activity patterns programmed into it and that complex movements are generated by activating appropriate combinations between the programs.
The same basic movement can be done in a variety of ways involving different muscles → motor equivalence .
Response chunking hypothesis → exercise combines central sensorimotor programs that control individual responses into programs that control behavioral sequences ( chunks ).

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